This invention pertains to valves and, particularly to valves used in processing systems which require the product to be kept in a sterile state.
Typical prior art aseptic valves comprise a body that supports a valve actuator. The actuator is adapted to reciprocate a stem to which a valve disk is attached that is movable toward and away from a seat to thereby alternately stop and permit flow of product through an opening surrounded by the seat. Generally, the valve stem is provided with one or more o-rings where it passes through the bonnet to prevent leakage of the pressurized product and prevent influx of contaminants from the environment to the body of the valve. The valve stem in aseptic valves customarily passes through a jacket on the bonnet through which steam at higher than atmospheric pressure flows to act as a positive barrier against migration of such contaminants as bacteria along the stem to its o-ring. The o-ring or rings on the stem are required to perform the dual functions of resisting steam pressure on one side and product pressure on the side, where the pressures are usually unbalanced, to thereby prevent leakage in either direction. O-rings, particularly after having aged, can lose their sealing capability. Thus, it is necessary to replace them occasionally, usually on a regular maintenance schedule. Moreover, as the o-ring size is increased to improve the seal, friction increases and more power or effort is required on the part of the actuator to reciprocate the valve stem.
Usually a spherical disk or plug is mounted to the stem for being engaged and disengaged with the valve seat so the plug makes circular line contact with the seat. Generally the diameter of the spherical plug is mated to the diameter of the seat surrounding the port which means that any given disk or plug design is dedicated to a particular valve seat size such that it is not feasible to use one plug in a valve of another size.
Prior art aseptic valves also required an aseptic joint which in effect was a pipe clamp for connecting the valve body and actuator bonnet together with a steam chamber around the clamp with inlet and outlet fittings to sterilize the joint. A prior art valve construction of this type is shown in U.S. Pat. No. 3,633,607. In addition in valves of this type a stem seal was required in the actuator bonnet of the valve rather than in the body and the stem seal moved during use into a zone in the bonnet that required sterilization.